Reviewed: Silva ML, Bernardo MA, Singh J, de Mesquita MF. Cinnamon as a complementary therapeutic approach for dysglycemia and dyslipidemia control in type 2 diabetes mellitus and its molecular mechanism of action: A review. Nutrients. July  2022;14(13):2773. doi: 10.3390/nu14132773.

By Shari Henson

Early detection and treatment are key factors in managing type 2 diabetes mellitus (T2DM) and avoiding complications. Some bioactive compounds from medicinal plants have been shown to exert antidiabetic activity through their ability to lower glucose levels. Previous studies have reported that cassia (Cinnamomum aromaticum syn. C. cassia, Lauraceae) or cinnamon (Cinnamomum verum syn. C. zeylanicum) supplementation can exert hypoglycemic effects in people with T2DM, but other studies report conflicting results. In this narrative review, the authors provide an overview of the potential beneficial effects of cinnamon in exerting control of dysglycemia (abnormal blood glucose levels) and dyslipidemia in people with T2DM and summarize cinnamon’s mechanisms of action. (The authors referred to all Cinnamomum species in the article as “cinnamon.”)

The authors searched PubMed, Medline, and Cochrane Library databases from January 2000 until May 2022 for relevant studies that included males and non-pregnant females aged 18 years or older who had been diagnosed with T2DM, impaired glycemia, or metabolic syndrome. The studies included experimental and/or quasi-experimental clinical trials, with or without control groups, and in which the intervention was cinnamon extract or powder. The variables analyzed in the studies included fasting/postprandial blood glucose, glycated hemoglobin, and lipid and anthropometric (e.g., body mass indices, body fat percentages) parameters.

The search yielded 771 potential articles, and 45 met the inclusion criteria. After analyzing the papers, the authors selected 14 articles on the effects of cassia or cinnamon on glycemia and nine articles on lipid profiles. The sample sizes in the studies ranged from 22 to 140, and study durations ranged from 40 days to four months.

Reviewed studies assessed multiple Cinnamomum species, including C. aromaticum, C. burmannii, C. cassia, C. verum, C. zeylanicum, and unspecified “cinnamon” powders. Importantly, Table 1 in the article, which summarizes selected studies on “the effects of cinnamon on glycemia and lipid profiles,” does not include every study mentioned in the paper. Table 1 lists 15 studies, including studies using cassia (n = 8), cinnamon (n = 2), and unspecified cinnamon species (n = 5), and all studies evaluated at least one blood sugar parameter. In addition, two studies on blood sugar were not listed in Table 1. The authors did not explain these discrepancies.

Of the 14 articles relating to blood glucose regulation in people with T2DM, eight reported that cassia or cinnamon improved fasting and postprandial blood glucose levels. The other six trials reported no beneficial effects of cassia or cinnamon. Only five of these studies used control groups.

Of the nine articles that assessed the effects of cassia or cinnamon on lipid profiles, one study reported decreased triglyceride and total cholesterol levels after 40 days of cinnamon supplementation, and two studies reported significantly decreased triglyceride levels after two or three months. The six other studies, which had similar durations, concluded that cinnamon had no beneficial effects on lipid profiles in diabetic patients.

In some studies of people with diabetes, cinnamon supplementation was associated with reduced plasma levels of the inflammation markers C-reactive protein, interleukin-6, and nitric oxide, while in other studies, concentrations of these markers did not significantly change. The results of the effects of cinnamon on oxidative stress markers were also mixed; some studies reported improved antioxidant enzyme activity and antioxidant power by ferric reduction, while others found no beneficial effects on total antioxidant capacity.

Different mechanisms of action have been proposed for cinnamon and its bioactive compounds, which include, among others, cinnamaldehyde, procyanidin type-A polymers, cinnamic acid, and coumarin. According to the authors, the main mechanism of action through which cinnamon improves dysglycemia is by the regulation of glucose metabolism in tissues via an insulin-mimetic-like effect. This effect is thought to be achieved through the regulation of insulin signaling pathways. The mechanism of action by which cinnamon and its constituents regulate lipid metabolism is not well understood; however, it may be related to the regulation of lipid metabolism in enterocytes (intestinal absorptive cells). Some bioactive compounds in cinnamon may lower the absorption of cholesterol and fatty acids in gut cells.

The authors speculated that the conflicting results of the reviewed studies may be due to the use of various doses, extracts, different Cinnamomum species, and forms of administration. Results also may have been influenced by different study designs, including different durations and the concurrent use of oral antidiabetic drugs in some studies.

“Targeted cinnamon-based therapy can provide an opportunity to modulate glucose and lipid dysregulation in order to avoid the progression of T2DM,” the authors concluded. “Cinnamon can also contribute as an antioxidant and an anti-inflammatory agent.”

Because of mixed results seen in this review, the authors recommend that the effects of cinnamon, using standardized randomized clinical trials with a larger number of participants, should be investigated to provide a comprehensive impact of cinnamon on people with diabetes and “a dose-response relationship should be explored, taking into account that it is an important factor in disease prevention and/or treatment strategies.”